1. Technical Field
The present invention relates to a base station, an interference control method, and a radio communication system, and more particularly to a base station, an interference control method, and a radio communication system, which conduct an interference control in locating plural micro base stations in an autonomous interference distribution control of a cellular radio communication system, particularly, a cellular radio communication system employing an orthogonal frequency division multiple access (OFDMA) system.
2. Background Art
In recent years, frequency division duplex (FDD) cellular radio communication systems employing the OFDMA system have been actively developed. In Japan, the cellular radio communication system employing the OFDMA is called “the 3.9 generation radio communication system”. As typical standards, there are a long term evolution (LTE) and an ultra mobile broadband (UMB), and those standards LTE and UMB have been globally standardized by industry associations such as 3rd generation partnership project (3GPP) and 3GPP2, respectively.
In the radio communication system, a terminal accesses to a radio network configured by a base station and a core network. An area covered by the base station is called “cell”, and may be called “macro cell”, “pico cell”, or “femto cell” according to a size of a cell radius thereof. As a basic communication means, the terminal that belongs to the base station issues a request to the base station to realize a call to another terminal belonging to the same base station or another base station over the core network. Likewise, a data communication is realized by allowing the terminal to issue a request to the base station.
In the radio communication system using the OFDMA, there has been known that a communication quality is deteriorated by a radio wave interference from a neighbor cell. In particular, in a cell edge, an interference power level from the neighbor cell and a desired signal level from a subject cell compete with each other, and it becomes clear as the deterioration of a Signal to Interference and Noise power Ratio (SINR) which is one of indexes representing, for example, a channel quality. In order to improve a capacity of not only the cell edge but also an overall system, it is important to mitigate an interference between the neighbor cells. For that reason, there has been known that the application of a fractional frequency reuse (FFR) is effective, which is a technique in which a frequency band that enables a radio signal to be transmitted with a high power between the neighbor cells is divided to cover the cell edge (an end of cell) with the divided frequency band. With the application of the FFR, a cell center terminal and a cell edge terminal are distinguished from each other to adjust an assignment and electric power of a radio resource. If there is no FFR, an equal electric power is transmitted over a full band (f0) so that scheduling can be conducted between a cell center (close to base station) and the cell edge without prejudice. However, a large interference occurs between the neighbor cells in the cell edge. Under the circumstances, the frequency band (f0) is divided into respective frequency bands (f1, f2, f3), and the electric powers that can be output in the respective frequency bands are adjusted, and a combination of the frequencies (f1, f2, f3) is appropriately selected for each cell so that the interference between the neighbor cells can be suppressed.